Bernie Legacy Prius owner

In a Toyota Hybrid the 12 volt battery keeps all the electrical system running while your car is parked. This includes the security system, the key fob sensors, the clock, and the memory in many of the computer systems. This is a fairly small drain but it builds up 24 hours a day 7 days a week. It also has to have enough power to start up the computer and everything else that was left on before the high voltage battery system is turn on. Once the high voltage battery system is turned on a high voltage to 12 volt converter turns on that produces about 14 volts. At this voltage the sealed 12 volt battery charges and will not over charge but it is a slower charge rate than you might be used to. The reason the high voltage battery is not used for this load when the car is park is that it could easily drain the high voltage battery enough to shorten its life. So if you leave you car parked to long the 12 volt battery gets sacrificed and it is fair cheaper to replace. Since we are talking about replacement, lead acid batteries come with a chemistry configured to produce lots of cranking amps (not needed in a hybrid because the high voltage battery pack cranks the engine) and deep discharge batteries that produce fewer amps but can be draw down many more times before they fail. The deep discharge type is the better choice in a hybrid because that is all it does. It gets slowly discharged when the car is parked. optima-smilling-short.bmp